Hydrolysis of inulin



Patented Feb. 1, 1927.

. UNITED STATES/PATENT OFFICE.

WILLIAM o. ansnm, or, scnnnncranr, NEW YORK, assrenon To innnsrnmreenmcs conrona'rron, or SCHENECTADY, NEW YORK, A coaronarron or newYORK.

nrnnomzs'rs on munm.

No Drawing. Original application filed July 12, 1321, Serial No.484,158. Divided andthis application i filed August 14, 1824. Serial No.731,966.

This invention relates to an improved method of preparing fructose frominuhn and to an improved'product resulting from the application of thisferred form. y i

The method of the present invention is applicable to inulin-containingmaterials of any kind but preferably it is apphed to clarified andurified-inulinsolutions obtained from the uice of thedahlia bulb inaccordance with the methodsdescribed in my'copending applications,Serial No. 369,537 and Serial No. 424,459. When the improved method isapplied in its preferred form to pure inulin, prepared accordingytothese processes, the final fructose sugar product obtained is of unusualpurity and 1s especiallysuitable for consumption as atood and alsopossesses unusually good keeping qualities. I a 7 Many attempts havehitherto been made to pre are a low cost sugar in the form of syrup,crystals, powder or the like, .WlllCll could hesubstituted for sucrose(i. erbeet or cane sugar) for certain important uses such as thereparation of soda syrups and soft drin s, the preservation of fruits,the manufacture o'f confectionery, for general cooking purposes, fortable use an only partially successful. The non sucrose syrups preparedhitherto for commercial consumption, such as starch syrups, corn syrups,malt syrups and the like, and all the solid, powdered and partiallycrystalline products prepared from similar sources, have failed to meetthe requirements which a sugar must have in order to compete in themarket with cane andbeet sugar products for many 1n1- 40 portantcommercial purposes.

Thus, for example, none of the foregoing.

flavors which render them undesirable for many of the purposesmentioned. Thus in the preparation of carbonated or soft drinks methodin its protaste of the desired definiteness or purit and uniformity. Onthe contrary in suci instances the finished soda-syrup will have ofitsown.

similar par- 39 poses. But these attempts have been' at most it isdesirable that the syrup used shall have a definite and uniform flavor;If the stock syrup or sugar from which the sodarup is prepared has apeculiar or variable avor of 1ts own, it is not possible to prepare fromit (by adding a natural or artificial flavoring substance) asoda syruphaving a flavor or a mixed flavor and this will vary with the varyingflavor of the stock syrup with which the naturalor artificial flavoringmaterial or extract is mixed to produce the finished soda-syrup.

Likewise in the production of confectioncry and culinary productsuniformity and purity of flavor of the finished product is 7.

one of the most important requirements and therefore the sugar or syrupused must not possess a variable flavor and preferably should not have ahighly pronounced fla'vor n Furthermore, uniformity of color of all ofthe above mentioned finished products is an important additionalrequirement and for this reason stock syrups or sugars with a pronouncedor non-uniform or objectionable color of their own are not suitable forthese very important commercial uses. The various solid, powdered, andartially crystalline commercialv forms of t e nonsucrose productshitherto produced do not meet the foregoing requirements and in additionmost of them have also the undesirable property of absorbing moistureand becomlng more or less asty so that they cannot be readily handledMany of them also undergo ob ecti'onable decompositions," when anattempt is made to keep'them in storage for any considerable length oftime or when they are employedin cooking operations or in themanufacture of confectionery.

The product of the present invention fulfills all the foregoingrequirements t'o-an extraordinary. degree and does not possess any ofthe above mentioned objectionable qualities and particularly itpossesses the property of sweetness inmuch greater degree than even caneor beetsugar. It is almost, if not quite, as tree from objectionablecolored impurities as is ordinary refined cane sugar syrup, so that itmay be employed for all the purposes for which ordinary water-White canesugar'syrup is employed. Furthermore, in syrup form it may be cooked orboiled without discoloration. Also in syrup form or in crystalline orsolid form the fructose-sugar food-product of the present invention isresistant toward the attack of certain objectionable molds and bacteriaand therefore possess good keeping qualities.

Because of the ready availability and cheapness of the raw materialsused and the simplicity and economy of the method by means of which, thefinished product of the present invention is produced, it can bemanufactured at a very low cost.

The methods hitherto commonly employed for preparing pure fructose frominulin involve complicated and expensive methods of recrystallization,usually from alcohol. Such recrystallization or other purification ismade necessary because the older methods of hydrolysis yield discoloredproducts or products which contain hygroscopic,

deleterious or otherwise objectionable impurities and which aretherefore unsuited for many of the uses for which ordinary refined canesugar products are employed. This is true even when highly purifiedinulin is used.

These impurities are very diflicult to remove from the fructose bybleaching treatments, crystallization or similar methods and thereforeto obtain the fructose in even an approximately pure form by these oldermethods, it has been necessary to repeat the purification treatments agreat many times. The final yield of fructose so obtained is, therefore,so small that the cost of manufacturing by these older methods upon acommercial scale would be prohibitive.

The method of hydrolysis employed in producing the product of thepresent invention produces fructose of a high degree of purity directlyfrom the inulin and thus avoids all the foregoing difficulties anddisadvantages. It is based mainly upon a regulated hydrolysis of theinulin under definitely controlled conditions and in its preferred formthe hydrol sis is carried out with a selected acid and a so with adefinite range of concentration of the acid. One of the most importantfeatures of the improved method referred to is the adjustment of thetime of hydrolysis to varying concentrations of acid and to the varyingchemical nature of the acid. It has been found that highly advantageousresults are obtained by stopping the hydrolysis at the end of adefinitely determined period of time. In determining this correct timeof hydrolysis, account is taken, as already mentioned, not only of thechemical nature of the acid but also of the concentration of the acidand'also in certain instances of the temperature and res sure. Byconducting the hydrolysis in this manner the inulin is readilyhydrolyzed completely into fructose of a very high degree of purity anda solution of pure fructose is obtained directly from the inulinsolution without the necessity of resorting to the older elaborate andexpensive methods of purification or crystallization previouslymentioned. Moreover, in the preferred form of the invention, thefructose is obtained directly in the form of a hi hly concentrated syrupand thus the cost or evaporating the solution is entirely avoided.

In other methods sometimes employed in the hydrolysis of inulin, a greatdeal of uncertainty has existed as to the optimum duration of thehydrolysis in order to obtain best yields of fructose. Theseuncertainties in the older methods referred to are due in large part tothe circumstance that the intermediate hydrolytic products of inulin, aswell as the decomposition products, resulting from various sidereactions, all have properties which resemble those of fructose. If,therefore, one selects any convenient property of fructose and attemptsto determine the concentration of the fructose in the mixed solution bymeasurements of this property, the results obtained will represent theresultant value of this property for all of the substances present.Thus, for example, since many of the hydrolytic and decompositionproducts are optically active or possess the power to rotate the planeof polarized light, the measurement of this property,

as the hydrolysis progresses, does not always give a true measure of theconcentration of fructose in the solution but corresponds to theresultant rotation of the mixture of all the optically active substancespresent. The measurement of the reducing power of the solution, as ameans of following the prog' ress of hydrolysis, leads to similarconfusing results for a similar reason, namely, that the varioushydrolytic and decomposition products each has a characteristicreducingpower of its own and, therefore, the reducing power of the mixedsolution represents the resultant of that of all the substances producedby the solution, usually increases at the beginning of the hydrolysisand then later decreases. In other methods this first maximum negativevalue of rotation has frequently been taken to indicate the highestobtainable concentration of fructose in the solution. I have discovered,however. that this is not the case and that if the hydrolysis becontinued after this first maximum negative rotation is reached, thenegative value of the rotation again usually increases and passesthrough a second maximum. Similarly several different maximum values ofnegative rotation may be passed through during the course of thehydrolysis before the highest possible negative rotation is attained.Furthermore, I have found that when the hydrolysisis carried out inaccordance with the method of the present invention, this final maximumor'highest attainable negative rotation, corresponds very closely to themaximum theoretical rotation of the solution calculated upon the basisthat all of the inulin present in the solution is converted entirelyinto fructose. In this calculation the specific rotation [0:1 offructose is taken as minus ninety three degrees and the concentration ofinulin in the solution is calculated from the weight of purified inulindried to constant weight at 90 C., whichwas originally employed inmaking up the solution.

Fructose exists in two tautomeric forms which are probablystereoisomers, and are supposed to have the following formulae llhe betaform, which is the ordinary crystalline form of fructose in the purestate has a theoretical rotation of minus 1 35.5 at 20 (1., but whendissolved in Water a portion of the beta form is supposed to change overinto the alpha form, which has not been isolated as far as the applicantknows, but has a calculated rotation of -21 at 20 C. The net effectafter equilibrium is reachedis that the rotation of the mixture as awhole assumes an approximate value of about -93 at 20 C; and thispermanent or equilibrium value will be referred to in the claims as themaximum negative rotation. In this calculation the formula of inulindried under these conditions is taken as 36 82031 Y The foregoingmethods furn sh criteria for judging the extent of the hydrolysis ofinu-' lin to fructose and therefore furnish means of determiningthetotal amount of impurities present in any given. instance under theparticular conditions of hydrolysis employed. The-total amount of theseimpurities corresponds to the difference between the percentage ofinulin which is completely hydrolyzed to fructose and one hundred percent. I have found that these impurities are objectionable because theyinterfere with the subsequentcrystallization of fructose from solutionand also because they impart increased hydroscopic properties to thesolid fructose obtained by crystallization or by evaporation of thehydrolyzed solution completely to dryness, in accordance with methodssuch as that described in my copending application, Serial No. 369,537.Ioreover, in many instances certain-of these impurities, particularlythose formed by the decomposition of fructose after the latter has beenformed, produce objectionable discoloration of the solution and alsodiscolor the solid fructose obtained therefrom. Theyalso impart avariable or objectionable flavor to the product.

Also I have found that there is an optimum concentration fortany givenacid, by means of which substantiallypne hundred per cent conversion ofinulin to fructose can be obtained. A greater or smaller concen-.tration than this optimum concentration gives a poorer result. It hasnow been found I that to obtain a maximum conversion with a stronginorganic acid requires a greater optimum concentration of acPd thanwith an organic acid. Thus, for example, the optimum concentration forhydrochloric acid is approximately five hundredths normal, while withacetic acid the optimum concentration is only about six thousandthsnormal. \Vith hydrochloric acid of this optimum concentration, the,maximum conversion of inulin to fructose is reached in about five to tenminutes, whereas with acetic acid, of the above given optimumconcentration, eight hours are required to produce a maximum conversionof the inulin to fructose.

- Furthermore, I have discovered that the time required to reach amaximum conversion with any given acid bears a certain definite andfixed relation to the concentration of the acid and that for each kindof acid, keeping the inulin concentration constant, this optimum timerequired formaximum conversion increases as the concentration of theacid diminishes, in such a way that the logarithm of the reciprocal ofthe time is approximately proportional to the logarithm of the normalconcentration of the acid. In other words, the acid strength I plottedagainst the reciprocal of the corresponding time gives straight line onlogarithmic paper. A different line is obtained, of course, for each anapproximately kind of. acid. Furthermore, I have dis'covered that theresults obtained with-certain organic acids such as acetic, citric andtartaric acid and the like when plotted in this manner, give straightlines which are approximately parallel and which lierelative- 1y closetogether. In other words, I have discovered that for different acidsbelonging to this general class, approximately the saine may be bestexplained as follows.

uantitative relationship exists between diferent concentrations of theacid and the corresponding time required for producing the highestpossible conversion of inulin to fructose. This relationship may beapproximately expressed by means of the following equation:

Log. N =a log. %+log. b,

in which N represents the normality of the acid in the usual sense,assuming that only the first hydrogen ion of the acid is active, while Tis the time required for the highest possible yield, expressed in hoursand in which the constant a has a value between about 1, and theconstant 12 has a value varying between about .0075 and .03. Theforegoing relationship between concentration and time holds good fortemperatures between about C. and 120 C. and for pressures of about oneatmosphere.

This relationship is not seriously affected by changes in the originalconcentration of the inulin solution for concentrations greater thanabout eight per cent by weight.

While it is desired that the scope of the present invention shall not berestricted by any unproven assum tions as tothe exact chemical nature oft e reactions produced .during the hydrolysis by strong inorganic acids,such as hydrochloric acid, which form the subject matter of the presentapplication, it is believed that the wide differences which exist in theaction of strong inorganic acids and the weaker organic apligs e acid,it is thought, acts as a catalyst in the hydrolysis of inulin by virtueof the hydrogen ion concentration, while the failure of. any given acidto produce a one hundred per cent conversion under certain conditions orwith certain concentrations is believed to be due to a condensing actionof the undissociated molecules of the acid or of the anion upon theproducts of the hydrolysis of inu lin and particularly upon thefructose. In

'other words, at each stage of the hydrolysis there seem to be tworeactions going on which are opposed to each other in their effects, onereaction. producing hydrolysis of inulin, probably through severalintermediate. stages, and another reaction bringing about adecomposition or a condensation of the different hydrolytic products andparysis has been conducted under such conditions that the acid destroysthe frustose or the intermediate compounds forming hydro:copicsubstances such as levulosin, and also other decomposition products suchas humin, levulinic acid, formic acid, etc. is my belief also that theseveral different maxima of polarization already described, which areobtained during the course of the hydrolysis, correspond to maximumconcentrations of these principal intermediate hydrolytic compounds andI am convinced that this is the reason that the significance of thesedifferent maxima has hitherto een misunderstood resulting in a failureto obtain pure fructose directly from inulin as in the improved methodof the present invention.

Among the principal advantages of the improved fructose food-product ofthe present invention, as compared with similar products hitherto known,are its greater stability especially toward heat, its exceptionally goodkeeping qualities, and in solid or crystalline form its greater freedomfrom a tendency to cake or become asty when exposed to a moist or humidatmosphere. These special advantages of the new product particularly itsgreater stability toward heat and its improved keeping qualities are duein large part, I believe, to the unusual purity of the product and tothe nature and degree of its acidity. In some instances (andparticularly where good keeping qualities are especially desired) I havefound that these a vantageous properties can be increased by firsthydrolyzing the pure inulin with the limitedamount of acid as specifiedand then after the hydrolysis iscomplet'ed and the product has cooled,adding an additional amount of acid either to the syrup or to the solidor crystalline product obtained therefrom by evaporation orcrystallization, as i for example, by the method of evaporation andcrystallization described in my co-pending applications, Serial No.369,537 and Serial No. 424,459. Where the product is intended for consumtion as a food itself or as a constituent of a ood, I prefer to add aninnocuous or edible acid such as citric acid and preferably tartaricacid or an acid tartrate or the like. 7 v

In the manufacture of candy or confectionery and in many culinaryoperations where a sugar is employed, it is highly desirable that thesugar shall not decompose or darken in color when cooked or heated andthe, improved pure fructose food-product of the present invention meetsthese requirements in a much more satisfactory manner than any similarproduct hitherto known.

This application is a divisional ap lication of my co-pendingapplication, erial No. 484,153.

I claim:

lln

III.

10 lution containing 1. The method of convertin the inulin to fructosewhich comprises su jecting the solution containing purified .inulin 'tothe action of an inorganic acid present in the 5 solution in aconcentration corresponding to about five hundredths (.05) normality fora period of about five minutes.

2. The method of converting inulin to fructose which comprisessubjecting the sopurified inulin to the action of an inorganic acidpresent in the solution in a concentration correspondin to about fivehundredths (.05) normality or period of about five minutes at atemperature of about 100 C.

five hundredths (.05) normaity for a period 7 of about five minutes at atemperature of about 100 C. n In testimony whereof I affix my signature.

LIAM C. ARSEM.

